45 8 GENERAL BIOLOGY 



although not reached directly by a single external stimulus, 

 they are so connected with the peripheral circuits of the 

 body as to be within the reach of all; and they may be in- 

 fluenced by all. Just how the circuits of the upper brain 

 are influenced, we may not say, but apparently the results 

 of these influences are more lasting here than in other parts 

 of the nervous system. The effect of a given stimulus is no 

 longer an unvarying impulse and action. In the labyrinth 

 of brain paths the stimulus sets off the whole chain of im- 

 pulses that have followed upon it in the past and the 

 pleasurable or painful results of past experience are 

 recalled in memory along with the stimulus ; if pleasurable, 

 the natural impulses that go with the stimulus may be 

 allowed to go on to fulfillment; if painful, the neurones of 

 the new center possess the power to direct action into new 

 channels. 



A child on seeing for the first time a pretty bee upon the 

 window pane is impelled to catch it and examine it with his 

 hands. If allowed to do so, he learns something about bees, 

 by the most fundamental of educational methods by ex- 

 perience. The impulse to touch the bee and the painful 

 impressions that immediately follow become so intimately 

 associated in the accessory circuits of his brain that the next 

 time he sees a bee (or it may be, even a fly) , on the window 

 pane the sight of it immediately sets off, along with the im- 

 pulse to touch it, other countervailing impulses arising 

 out of the memory of the former experience. Thus the 

 new control center steps in and prevents the expected 

 action by initiating new ones. 



Perhaps we may be permitted to compare this new con- 

 trol center to the referee at a game. He is not necessary to 

 the progress of regular play, but he may with advantage 

 step in and control the action in case of conflict, or of the 

 appearance of unsolved difficulties. 



